A modern dusty Western, a twisty Hitchcock-ian thriller, a Cormac McCarthy-esque existentialist meditation on man, his internal crisis, an exploration of the price of fame and artistry, a slasher-like revenge picture, and even at times a black comedy, William Monahan’s ambitious, but overstuffed sophomore directorial effort, “Mojave,” wants to be several movies at once. While it has trouble working out which kind of movie it exactly is (answer: all of the above), its disparate elements do intermittently and effectively work. However, a shallow premise, pompously overwrought dialogue, and hit-and-miss execution make for an occasionally enjoyable, but not entirely convincing effort.

It’s difficult to engender audience sympathy by opening a movie with a white, wealthy, spoiled 20-something star, who is full of angst, complains about being famous since he was 18, and is in the midst of an experiential crisis at being on top of the mountain and achieving everything goal he’s ever sought. But this is how writer/director Monahan (the Oscar-winning screenwriter behind Martin Scorsese’s “The Departed”) chooses to begin his movie, and we soon realize B-movie genre dimensions trump sympathy or credibility (like a Hitchcock-ian protagonist pawn, we don’t need to like the character, he just needs to put the plot into motion).

The man in question is Thomas (Garrett Hedlund), a famous wunderkind actor/artist/filmmaker who’s in a spiritual funk and even harbors suicidal tendencies. He’s ashamed of his shallow Hollywood existence and his mounting personal clichés, including a torrid affair with his French female co-star (Louise Bourgin from Luc Besson’s “The Extraordinary Adventures of Adèle Blanc-Sec”) while his wife and daughter vacation abroad. Full of self-loathing, Thomas does what every other James Dean-like brooding figure does, he heads off into the Mojave desert to smoke cigarettes, clear his head, and maybe do something self-destructive. But his reckless sojourn into the void is quickly interrupted. One evening, over a campfire, a mysterious, hyper-literate drifter named Jack (Oscar Isaac), who has a propensity for psychobabble and mind games, stops by for some philosophical tête-à-tête. There’s an obvious air of danger around the stranger’s edges.

These alpha males engage in a tense back and forth volley of wits, ideals, and principles, with Jack quoting Shakespeare and George Bernard Shaw, and showing off his fierce intellect with a devilish Cheshire grin. But when discord between the two men erupts into violence, Jack is scorned and soon and a cat and mouse game of retribution develops.

Deep moral contours confuse matters too. In the fallout, as Thomas tries to escape the death rattle of the desert, an innocent is killed in the crossfire of his quickly escalating war with Jack, which complicates the celebrity’s clean getaway back to the Hollywood Hills.

Back in L.A. the movie becomes a moody, stalker-like thriller. The clock ticks as Thomas deals with his moral transgressions, Jack creeps into the city, slowing circling his prey like a shark, and we tensely await the sparks to fly. But “Mojave” is just too tonally inconsistent for all of this to work. For one, the film’s Hitchcock-ian score in the second half is way too on the nose and different musically from what we heard earlier. The mood shift is jarring.

Then there are the actors. Oscar Isaac spends the entire movie chewing the scenery with a grizzled and affected world-weary accent that feels strained and overdone. But what’s dark and menacing at first becomes wildly entertaining in the movie’s second half (you kind of want to see Isaac, who was also quite funny in “Ex Machina,” get cast in a full-on comedy already). And then there’s Hedlund’s humorless and dead-serious performance, like a mix of Johnny Depp, fuck-the-world bad boy-isms, and Kurt Cobain-like brooding (many a cigarette is smoked down to the nub, many tresses of hair are flipped).

The heightened sense of humor in “Mojave” develops as the movie moves forward, but you wish it was as aware of itself when it began. Walton Goggins co-stars as Thomas’ unscrupulous lawyer, and Mark Wahlberg really leans on his comic relief role — the shifty, Hollywood cliché dirtbag producer with the affinity for prostitutes — with perhaps too much flair.

“Mojave” is not without its highlights. Oscar Isaac can be a laugh riot at times, and the movie, overall, is a much more entertaining ride when it fully embraces its B-movie colors. But it’s constantly undone when its moody pretensions clash with its genre sensibilities.

Monahan clearly has a lot on its mind, and, frustratingly enough, there are some good ideas in his movie. It plays with concepts of fate being driven by chance — Hedlund being the lucky artist, Isaac the one fortune never fell on — the duality of man, the ego, and the self. “Mojave” toys with the metaphors of Jesus meeting the Devil in the desert and haunting his conscience as he goes back into society. Another reading of the movie could be Jack not existing at all, a figment of Thomas’ imagination, and another form of his soul-tormenting inner voice. But, unfortunately, “Mojave” just isn’t sophisticated enough to play on all of these levels. The movie is occasionally stimulating intellectually, but is otherwise ponderous and tired.

A weird, uneven mixed bag, there’s much about “Mojave” that’s paradoxically maddening and doesn’t really add up. As the plot becomes less interesting and more straight-forward — like a slasher movie with the evil antagonist character slowly closing in on the hero — it becomes fun and more purely enjoyable. Maybe Monahan was overburdened by trying to create a complex genre hybrid when something more streamlined and simple would have really done the trick. [C+]